Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K19/00—Liquid crystal materials
  • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
  • C09K19/38—Polymers
  • C09K19/3833—Polymers with mesogenic groups in the side chain
  • C09K19/3838—Polyesters; Polyester derivatives
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/68—Polyesters containing atoms other than carbon, hydrogen and oxygen
  • C08G63/685—Polyesters containing atoms other than carbon, hydrogen and oxygen containing nitrogen
  • C08G63/6854—Polyesters containing atoms other than carbon, hydrogen and oxygen containing nitrogen derived from polycarboxylic acids and polyhydroxy compounds
  • C08G63/6856—Dicarboxylic acids and dihydroxy compounds
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K19/00—Liquid crystal materials
  • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
  • C09K19/42—Mixtures of liquid crystal compounds covered by two or more of the preceding groups C09K19/06 - C09K19/40
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K19/00—Liquid crystal materials
  • C09K19/04—Liquid crystal materials characterised by the chemical structure of the liquid crystal components, e.g. by a specific unit
  • C09K19/42—Mixtures of liquid crystal compounds covered by two or more of the preceding groups C09K19/06 - C09K19/40
  • C09K19/46—Mixtures of liquid crystal compounds covered by two or more of the preceding groups C09K19/06 - C09K19/40 containing esters
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31786—Of polyester [e.g., alkyd, etc.]

Definitions

• This invention concerns novel liquid crystal polymers (LCP) materials, novel intermediates and methods for preparing them.
• LCP liquid crystal polymers
• Liquid crystals can exist in various phases. In essence there are three different classes of liquid crystalline material, each possessing a characteristic molecular arrangement. These classes are nematic, chiral nematic (cholesteric) and smectic. A wide range of smectic phases exists, for example smectic A and smectic C. Some liquid crystal materials possess a number of liquid crystal phases on varying the temperature, others have just one phase. For example, a liquid crystal material may show the following phases on being cooled from the isotropic phase :- isotropic - nematic - smectic A - smectic C - solid. If a material is described as being smectic A then it means that the material possesses a smectic A phase over a useful working temperature range.
• a smectic A phase When a smectic A phase is composed of chiral molecules, it may exhibit an electroclinic effect, i.e. a direct coupling of molecular tilt to applied field.
• the origin of the electroclinic effect in a smectic A phase composed of chiral polar molecules has been described by Garoff and Meyer as follows.
• the application of an electric field parallel to the smectic layers of such a smectic A phase biases the free rotation of the transverse molecular dipoles and therefore produces a non-zero average ofthe transverse component ofthe molecular polarisation.
• a tilt of the long molecular axis (the director) is induced in a plane pe ⁇ endicular to the dipole moment.
• a sample a tilt ofthe director is directly related to a tilt ofthe optic axis.
• the electroclinic effect results in a linear electro-optic response.
• the electro-optic effect can manifest itself as a modulation ofthe effective birefringence ofthe device.
• Electroclinic (EC) devices are useful, for example, in spatial light modulators having an output that varies linearly with applied voltage.
• a further advantage of EC devices is that they have high speed response times, much faster than twisted nematic type devices.
• One known type of ferroelectric device is bistable, in contrast the EC device is not bistable and has an output that varies linearly with applied voltage.
• the electroclinic effect is sometimes referred to as the soft-mode effect see G Andersson et al in Appl. Phys. Lett., 51, 9, (1987).
• S A * is meant a S A phase which contains some proportion of chiral molecules.
• Cholesteric or chiral nematic liquid crystals possess a twisted helical structure which is capable of responding to a temperature change through a change in the helical pitch length. Therefore as the temperature is changed, then the wavelength of the light reflected from the planar cholesteric structure will change and if the reflected light covers the visible range then distinct changes in colour occur as the temperature varies. This means that there are many possible applications including the areas of thermography and thermooptics.
• the cholesteric mesophase differs from the nematic phase in that in the cholesteric phase the director is not constant in space but undergoes a helical distortion.
• the pitch length for the helix is a measure of the distance for the director to turn through 360°.
• a cholesteric material is chiral material. Cholesteric materials may also be used in electro-optical displays as dopants, for example in twisted nematic displays where they may be used to remove reverse twist defects. They may also be used in cholesteric to nematic dyed phase change displays where they may be used to enhance contrast by preventing wave- guiding.
• thermochromic applications of cholesteric liquid crystal materials usually use thin film preparations of the materials which are then viewed against a black background. These temperature sensing devices may be placed into a number of applications involving thermometry, medical thermography, non-destructive testing, radiation sensing and for decorative purposes. Examples of these may be found in D G McDonnell in Thermotropic Liquid Crystals, Critical Reports on Applied Chemistry, Vol. 22, edited by G W Gray, 1987 pp 120-44; this reference also contains a general description of thermochromic cholesteric liquid crystals.
• thermochromic applications require the formulation of mixtures which possess low melting points, short pitch lengths and smectic transitions just below the required temperature-sensing region.
• the mixture or material should retain a low melting point and high smectic - cholesteric transition temperatures.
• thermochromic liquid crystal devices have a thin film of cholesterogen sandwiched between a transparent supporting substrate and a black absorbing layer.
• One ofthe fabrication methods involves producing an 'ink' with the liquid crystal by encapsulating it in a polymer and using printing technologies to apply it to the supporting substrate. Methods of manufacturing the inks include gelatin microencapsulation, US patent 3,585,318 and polymer dispersion. US patents 1,161.039 and 3,872.050.
• One of the ways for preparing well-aligned thin-film structures of cholesteric liquid crystals involves laminating the liquid crystal between two embossed plastic sheets. This technique is described in UK patent 2,143,323.
• Ferroelectric smectic liquid crystal materials which can be produced by mixing an achiral host and a chiral dopant, use the ferroelectric properties ofthe tilted chiral smectic C, F, G, H, I, J and K phases.
• the chiral smectic C phase is denoted S c * with the asterisk denoting chirality.
• the S c phase is generally considered to be the most useful as it is the least viscous.
• Ferroelectric smectic liquid crystal materials should ideally possess the following characteristics: low viscosity, controllable spontaneous polarisation (Ps) and an S c phase that persists over a broad temperature range which should include ambient temperature and exhibits chemical and photochemical stability.
• ferroelectric liquid crystal devices Materials which possess these characteristics offer the prospect of very fast switching liquid crystal containing devices.
• ferroelectric liquid crystal devices Some applications of ferroelectric liquid crystals are described by J S Patel and J W Goodby in Opt. Eng., 1987, 26, 273.
• ferroelectric liquid crystal devices the molecules switch between different alignment directions depending on the polarity of an applied electric field. These devices can be arranged to exhibit bistability where the molecules tend to remain in one of two states until switched to the other switched state.
• Such devices are termed surface stabilised ferroelectric devices, e.g. as described in US 5061047 and US 4367924 and US 4563059. This bistability allows the multiplex addressing of quite large and complex devices.
• One common multiplex display has display elements, i.e. pixels, arranged in an X. Y matrix format for the display of for example alpha numeric characters.
• the matrix format is provided by forming the electrodes on one slide as a series of column electrodes, and the electrodes on the other slide as a series of row electrodes. The intersections between each column and row form addressable elements or pixels.
• Other matrix layouts are known, e.g. seven bar numeric displays.
• a common feature involves the application of a voltage, called a strobe voltage to each row or line in sequence.
• a voltage called a strobe voltage
• data voltages are applied to all column electrodes.
• the differences between the different schemes lies in the shape ofthe strobe and data voltage waveforms.
• the material may be switched between its two states by two strobe pulses of opposite sign, in conjunction with a data waveform.
• a blanking pulse may be used to switch t e material into one of its states. Periodically the sign ofthe blanking and the strobe pulses may be alternated to maintain a net d.c. value. These blanking pulses are normally greater in amplitude and length of application than the strobe pulses so that the material switches irrespective of which ofthe two data waveforms is applied to any one intersection. Blanking pulses may be applied on a line by line basis ahead of he strobe, or the whole display may be blanked at one time, or a group of lines may be simultaneously blanked.
• Devices can be assessed for speed by consideration ofthe response time vs pulse voltage curve. This relationship may show a minimum in the switching time ( ⁇ at a particular applied voltage (V m ⁇ n )- At voltages higher or lower than V m ⁇ n the switching time is longer than t-,,,-,. It is well understood that devices having such a minimum in their response time vs voltage curve can be multiplex driven at high duty ratio with higher contrast than other ferroelectric liquid crystal devices. It is preferred that the said minimum in the response time vs voltage curve should occur at low applied voltage and at short pulse length respectively to allow the device to be driven using a low voltage source and fast frame address refresh rate.
• Typical known materials which do not allow such a minimum when included in a ferroelectric device include the commercially available materials known as SCE13 and ZLI-3654 (both supplied by Merck UK Ltd. Poole, Dorset).
• a device which does show such a inimmum may be constructed according to PCT GB 88/01004 and utilising materials such as e.g. commercially available SCE8 (Merck UK Ltd).
• Other examples of prior art materials are exemplified by PCT/GB 86/00040, PCT GB 87/00441 and UK 2232416B.
• the unit that is the basic building block of a polymer is called a monomer.
• the polymerisation process i.e. the formation of a polymer from its constituent monomers does not usually create polymers of uniform molecular weight, rather what is created is a distribution of molecular weights.
• D.P degree of polymerisation
• a number of different average molecular weights can be drawn from gel permeation chromatography (GPC) for a given sample including: M n - number average molecular weight and M w - weight average molecular weight.
• the value used to calculate D.P. is usually M n and polydispersity is usually defined as My/M,,.
• Polymers can be made from different types of monomers, in which case the polymer is called a co-polymer. If two types of monomer join in a random fashion then the polymer is called a random co-polymer. If the two monomers form short sequences of one type first which then combine to form the final polymer then a block copolymer results. If short sequences of one of the monomers attach themselves as side chains to long sequences consisting of the other type of monomer then the polymer is referred to as a graft copolymer.
• liquid crystal (LC) polymers the monomers can be attached together in essentially two ways.
• the liquid crystal part or mesogenic unit of the polymer may be part of the polymer backbone resulting in a main chain LC polymer.
• the mesogenic unit may be attached to the polymer backbone as a pendant group i.e. extending away from the polymer backbone: this results in a side-chain LC polymer.
• These different types of polymer liquid crystal are represented schematically below. The mesogenic units are depicted by the rectangles.
• the side chain liquid crystal polymer can generally be thought of as containing a flexible polymer with rigid segments (the mesogenic unit) attached along its length by short flexible (or rigid) units. It is the anisotropic, rigid section of the mesogenic units that display orientational order in the liquid crystal phases. In order to affect the phases exhibited by the liquid crystal and the subsequent optical properties there are many features which can be altered, some of these features are particularly pertinent to side-chain liquid crystal polymers.
• One of these features is the flexible part that joins the mesogenic unit to the polymer backbone which is generally referred to as the spacer group. The length and flexibility of this spacer group can be altered.
• a number of side-chain liquid crystal polymers are known, for example see GB 2146787 A.
• Liquid crystal polyacrylates are a known class of liquid crystal polymer (LCP).
• LCPs are known and used in electro-optic applications, for example in pyroeiectric devices, non-linear optical devices and optical storage devices. For example see GB 2146787 and Makromol. Chem. (1985) 186 2639-47.
• (CH 2 ) m is the flexible spacer group and X is the side-chain mesogenic unit and R is hydrogen or alkyl.
• Patent Application PCT GB 94/00662 describes amongst other things the use of tlie Baylis- Hillman Reaction to make a range of novel liquid crystal polymers.
• a method for the preparation of polyacrylate homo- or co-polymers having the following repeat unit is described in UK patent application GB 9203730.8
• Ri and R 2 are independently alkyl or hydrogen, R 3 is alkyl, hydrogen or chlorine, m is O or an integer 1-20, W is a linkage group COO or OOC or O and X is a mesogenic group.
• liquid crystal polymers are extremely difficult to align in devices.
• two techniques which have been used for aligning liquid crystal polymers. It is possible to try to align the liquid crystal polymer in a similar manner as a low molar mass liquid crystal, which is described in more detail below.
• mechanical techniques can be used such as shearing. Typically mechanical shearing is performed over hot rollers, this technique is generally only suitable for flexible substrates. It is possible to shear a sample between glass slides however the glass slides cannot be sealed in the conventional manner.
• the technique for aligning low molar mass liquid crystals is typically as follows.
• Transparent electrodes are fabricated on the surfaces ofthe substrates, the substrates typically being made of glass e.g. glass slides.
• an alignment process is necessary for both substrates.
• a thin alignment layer is deposited to align the liquid crystal molecules, typically either organic or inorganic aligning layers are used, for example SiO deposited by evaporation is a typical inorganic alignment layer.
• One method to form the alignment layer involves rubbing the surface by textures or cloths.
• Polyimides have also been employed for the surface alignment of layers. Polyimide is coated onto the substrates bearing electrodes by a spinner and then cured to form a layer of approximately 50nm thickness.
• each layer surface is repeatedly rubbed in substantially one direction with an appropriate material. If the liquid crystal molecules are deposited on this layer they are automatically aligned in the direction made by the rubbing. It is often preferable if the molecules possess a small angle pre-tilt typically 2-3°. Higher pre-tilts are sometimes required.
• the two substrates are then fixed together for example by adhesive and are kept separate by spacing materials. This results in uniform and accurate cell spacing.
• a typical adhesive is an epoxy resin.
• This sealing material is usually then precured.
• the electrodes may then be precisely aligned for example to form display pixels.
• the cell is then cured at, for example 100- 150°C. At this point the empty liquid crystal cell is complete.
• the cell is filled with the liquid crystal material.
• the opening size in the sealing area of the liquid crystal cell is rather small therefore the cell can be evacuated, for example in a vacuum chamber, and the liquid crystal material forced into the cell via gas pressure. More than one hole in the sealing area may be used.
• the empty cell is put into a vacuum chamber and then the vacuum chamber is pumped down.
• the open region of the sealant is dipped into the liquid crystal material and the vacuum chamber is brought back to normal pressure.
• Liquid crystal material is drawn into the cell as a result of capillary action, external gases can be applied to increase the pressure.
• the filling process is complete the hole or holes in the sealant is are capped and the cell is cured at a temperature above the liquid crystal material clearing point to make the liquid crystal molecular alignment stable and harden the capping material.
• Polymer liquid crystal molecules tend to be more viscous than low molecular weight liquid crystal materials and are therefore more difficult to align and more difficult to fill into devices. Only liquid crystal polymers with low molecular weights can be flow filled into a cell, and once a degree of polymerisation greater than around 30 or 40 repeat units is reached, most liquid crystal polymers become so viscous that flow filling cells is extremely difficult. Much slower cooling is needed in order to try and align liquid crystal polymers and this usually results in poor uniformity of alignment.
• the response time is dependent on a number of factors, one of these being the spontaneous polarisation, denoted Ps (measured in nC cm " ).
• Ps the spontaneous polarisation
• Ferroelectric smectic liquid crystal materials which can be produced by mixing an achiral host and a chiral dopant, use the ferroelectric properties of the tilted chiral smectic C, F, G, H, I, J, and K phases.
• the chiral smectic C phase is denoted S c * with the asterisk denoting chirality.
• the S c * phase is generally considered to be the most useful as it is the fastest switching.
• the material should exhibit a long pitch chiral nematic (denoted N*) and S A phase at temperatures above the chiral smectic phase in order to assist surface alignment in a device containing liquid crystalline material.
• Ferroelectric smectic liquid materials should ideally possess the following characteristics: low viscosity controllable Ps and an S c * phase that persists over a broad temperature range, which should include ambient temperature, and exhibits chemical and photochemical stability. Materials which possess these characteristics offer the prospect of very fast switching liquid crystal containing devices.
• Ferroelectric LCDs by Dijon in Liquid Crystals Applications and Uses, vol. 1 Ed. Bahadur. World Scientific Publishing Co. Pte. Ltd, 1990 pp 350-360 and references therein discusses alignment processes for smectic phases for low molar mass materials. The filling of cells is believed to be possible only in the isotropic or nematic phase due to the viscosity of smectic phases. Generally materials with the following phase sequence give good alignment:
• X,- X 5 are independently selected from H, F, Cl. NO 2 , CF 3 , OR, R, SR, -f-CO- or
• R is C M 5 branched or straight chain alkyl; provided that one of X r X 5 is selected from -CO- or -f-OC- ; p is at least 2;
• T, T 2 , T 3 , T 4 are independently selected from H, F, Cl, NO 2 , CF 3 , OR, R, SR, where R is
• X is selected from CO 2 and OOC; n is selected from 1-5; m is selected from 1-20; Y is selected from O, S, CH 2 , CO 2 , OOC;
• rings A, B and C are independently selected from phenyl, cyclohexyl and pyrimidine and may be independently of each other substituted with at least one of Cl or F;
• linking groups A and B may be selected from single bond CO 2 , OOC provided that if ring B is not present then at least one of A or B is a single bond;
• rings A, B and C are all selected from phenyl and preferably at least one ofthe rings A.
• B or C has at least one F present.
• X is C0 2 .
• n 1
• Y is O.
• links A and B are single bonds.
• W if present, is a single bond.
• T,-T 4 are selected from H and F.
• Z is CN
• the materials ofthe present invention may be any of the known types of polymer including homo-polymers or co-polymers.
• Figure 1 synthetic scheme for the preparation of compounds described by the current invention.
• Figure 2 illustrates a liquid crystal device
• Figure 3 illustrates a pyroeiectric device
• Figures 4 and 5 illustrate front and sectional views respectively of a reflective spatial light modulator drawn to different scales, in which the materials ofthe current invention may be inco ⁇ orated.
• Figure 6 illustrates an electrochemical device in which the materials ofthe current invention may be inco ⁇ orated.
• the diol (2.5mmol) and an equimolar amount ofthe respective acid chloride (2.5mmol) were subjected to polymerisation by melt condensation in Schlenk tubes using a magnetic stitrrer.
• the reactants were maintained in molten condition under a constant weak nitrogen stream which was used to remove the HCl evolved in the reaction.
• the temperature was increased to 120°C, and then after a further 2h the pressure was reduced to 1 Omm Hg.
• the presuure was reduced to 0.1 mm Hg at the same temperature. Finally the temperature was increased to 160°C over 2-3h.
• the final products were isolated by repeatedly dissolving the materials in dichloromethane followed by subsequent precipitation ofthe polymeric/oligomeric materials by addition to methanol, until no monomer content was detectable by chromatographic methods.
• the chemical structures of the polymers were characterised using conventional spectroscopic methods.
• Detection ofthe eluting samples was made by an ERMA ERC 7510 refractive index detector.
• the GPC curves were calibrated against linear polystyrene standards.
• the temperature was controlled to +/- 0.5°C by placing the samples in a microfumace equipped with a Eurotherm EPC 900 temperaure controlling unit.
• the structural features and the GPC data for the polymers are shown in Table 1.
• the degree of polymerisation for all of the polymers lies between 13 and 15 repeat units.
• the polydispersity ofthe samples is more or less similar and therefore comparisons between different polymers are possible.
• the comparatively low polydispersity is a result ofthe good solubility ofthe monomers and low molar mass oligomers in methanol.
• ⁇ Mn> and the polydispersity ( ⁇ Mw>/ ⁇ Mn>) were determined by GPC.
• DP degree of polymerisation.
• the liquid crystal device consists of two transparent plates, 1 and 2, for example made from glass. These plates are coated on their intemal face with transparent conducting electrodes 3 and 4.
• An alignment layer 5,6 is introduced onto the intemal faces of the cell so that a planar orientation of the molecules making up the liquid crystalline material will be approximately parallel to the glass plates 1 and 2. This is done by coating the glass plates 1,2 complete with conducting electrodes so that the intersections between each column and row form an x, y matrix of addressable elements or pixels.
• the alignment directions are orthogonal.
• the layers 5,6 Prior to the construction of the cell the layers 5,6 are rubbed with a roller covered in cloth (for example made from velvet) in a given direction, the rubbing directions being arranged parallel (same or opposite direction) upon construction of the cell.
• a spacer 7 e.g. of polymethyl methacrylate separates the glass plates 1 and 2 to a suitable distance e.g. 2 microns.
• Liquid crystal material 8 is introduced between glass plates 1,2 by filling the space in between them. This may be done by flow filling the cell using standard techniques.
• the spacer 7 is sealed with an adhesive 9 in a vacuum using an existing technique.
• Polarisers 10, 11 may be arranged in front of and behind the cell.
• Alignment layers may be introduced onto one or more of the cell walls by one or more of the standard surface treatment techniques such as rubbing, oblique evaporation or as described above by the use of polymer aligning layers.
• the substrates with the aligning layers on them are heated and sheared to induce alignment
• the substrates with the aligning layers are thermally annealed above the glass transition temperature and below the liquid crystal to isotropic phase transition in combination with an applied field.
• Further embodiments may involve a combination of these aligning techniques. With some of these combinations an alignment layer may not be necessary.
• the device may operate in a transmissive or reflective mode. In the former, light passing through the device, e.g. from a tungsten bulb, is selectively transmitted or blocked to form the desired display. In the reflective mode a mirror, or diffuse reflector, (12) is placed behind the second polariser 11 to reflect ambient light back through the cell and two polarisers. By making the mirror partly reflecting the device may be operated both in a transmissive and reflective mode.
• the alignment layers 5,6 have two functions, one to align contacting liquid crystal molecules in a preferred direction and the other to give a tilt to these molecules - a so called surface tilt - of a few degrees typically around 4° or 5°.
• the alignment layers 5,6 may be formed by placing a few drops ofthe polyimide on to the cell wall and spinning the wall until a uniform thickness is obtained. The polyimide is then cured by heating to a predetermined temperature for a predetermined time followed by unidirectional rubbing with a roller coated with a nylon cloth.
• a single polariser and dye material may be combined.
• the liquid crystal material 8 when introduced into the cell may consist of liquid crystal polymer or consist of liquid crystal monomers and a photoinitiator. It may also contain a reagent which will limit the molecular weight of the polymer for example a chain transfer reagent and it may also include a thermal initiator.
• the monomer material may be aligned before polymerisation using standard techniques, for example by heating up to and cooling from the isotropic phase or from a liquid crystal phase such as a nematic or chiral nematic phase. It is also possible that the liquid crystal polymer may be aligned by one or more techniques including the use of surface forces, shear alignment or field alignment.
• polymerisation there may still be some amount of monomer material remaining. This may be unreacted monomer or low molar mass additives which do not bear polymerisable groups.
• Polymerisation may be carried out by using any of the known techniques. For example the monomer material plus initiator may be exposed to UV light, heat may also be applied to permit polymerisation within a given phase ofthe monomer and/or polymer.
• the polymerisation process may take place in the presence of heat and a thermal initiator.
• this technique it may be preferable if it is carried out at a temperature which corresponds to a liquid crystal phase ofthe monomer material.
• Many ofthe compounds described by formula I and mixtures including compounds of formula I show liquid crystalline behaviour and are thus usefully employed in liquid crystal devices.
• Example of such devices include optical and electro-optical devices, magneto-optical devices and devices providing responses to stimuli such as temperature changes and total or partial pressure changes.
• the compounds of formula I may also be included in a mixture, where the mixture comprises at least two compounds.
• Typical mixtures include mixtures consisting of compounds of formula I and also mixtures comprising at least one compound of formula I and at least one compound not of formula I.
• Devices which use a liquid crystal material as the optical storage medium are an important class of such devices.
• the use of semiconductor lasers, especially As lasers where x is from 0 to 1, and is preferably 1, has proven popular in the above applications because they can provide laser energy at a range of wavelengths in the near infra-red which cannot be seen and thus cannot interfere with the visual display, and yet can provide a useful source of well-defined, intense heat energy.
• Gallium arsenide lasers provide laser light at wavelengths of about 850nm, and are useful for the above applications. With increasing Al content (x ⁇ 1 ), the laser wavelength may be reduced down to about 750nm. The storage density can be increased by using a laser of shorter wavelength.
• the compounds ofthe present invention may be suitable as optical storage media and may be combined with dyes for use in laser addressed systems, for example in optical recording media.
• the smectic and/or nematic properties ofthe materials described by the current invention may be exploited.
• the materials of the present invention nay be used in ferroelectric mixtures and devices.
• the compounds ofthe present invention may also be used in pyroeiectric devices for example detectors, steering arrays and vidicon cameras.
• Figure 3 illustrates a simple pyroeiectric detector in which the materials ofthe present invention may be inco ⁇ orated.
• a pyroeiectric detector consists of electrode plates 13,14 at least one of which may be pixellated. In operation the detector is exposed to radiation R, for example infrared radiation, which is absorbed by the electrode 13. This results in a rise in temperature which is transmitted to a layer of pyroeiectric material 15 by conduction, The change in temperature results in a thermal expansion and a charge is generated. This change in charge is usually small when compared with the charge output due to the change in the spontaneous polarisation, Ps with a change in temperature; this constitutes the primary pyroeiectric effect. A change in charge results in a change in potential difference between the electrodes. The charge on each pixel may be read out and the resulting signal is used to modulate scanning circuits in, for example, a video monitor and for a visual image ofthe infra red scans.
• R for example infrared radiation
• a spatial light modulator comprises a liquid crystal cell 16 formed by typically two glass walls 1 and 2 and 0.1-10 ⁇ m e.g. 2.5 ⁇ m thick spacer 7. The inner faces ofthe walls carry thin transparent indium tin oxide electrodes 3,4 connected to a variable voltage source 17.
• ⁇ layers 5.6 On top ofthe electrodes 3,4 are surface alignment layers 5.6 e.g. of rubbed polyimide described in or detail later. Other alignment techniques are also suitable e.g. non-rubbing techniques such as evaporation of SiO 2 .
• a layer 8 of liquid crystal material is contained between the walls 1,2 and spacer 7.
• a linear polariser 11 In front ofthe cell 16 is a linear polariser 11; behind the cell 16 is a quarter plate 18 (this may be optional) and a mirror 19.
• An example of a linear polariser is a polarising beam splitter ⁇ not illustrated here).
• electroclinic devices there are a variety of electroclinic devices in which the compounds of the present invention may be inco ⁇ orated.
• active back plane driving may be utilised.
• One ofthe walls forming the cell may be formed from a silicon substrate e.g. a wafer which possesses circuitry for driving pixels.
• liquid crystal display devices for example chiral smectic electro-optic devices.
• Such a device may comprise a layer of liquid crystal material contained between two spaced cell walls bearing electrode structures and surface treated to align liquid crystal material molecules.
• the liquid crystal mixtures may have many applications including in ferroelectric, thermochromic and electroclinic devices.
• the compounds of the present invention may be mixed with each other to form useful liquid crystal mixtures, they may also be used with other liquid crystal polymers or low molar mass non-polymer liquid crystal materials.
• Suitable devices in which the materials of the current invention may be inco ⁇ orated include beam steerers, shutters, modulators and pyroeiectric and piezoelectric sensors.
• the materials of the present invention may also be useful as dopants in ferroelectric liquid crystal devices, which may be multiplexed, or they may be used in active backplane ferroelectric liquid crystal systems.
• the materials of the present invention may also be useful as host materials.
• the materials of the present invention may be included in mixtures which also contain one or more dopants.
• Compounds of formula I may be mixed with a wide range of hosts, for example smectic hosts to form a useful liquid crystal composition. Such compositions can have a range of Ps values.
• Compounds of formula I may be mixed with one or more ofthe types of hosts Vlll-Xffl. These different types of hosts may be mixed together to which the compound of general formula I may also be added.
• Typical hosts include:
• R, and R 2 are independently C 3 -C 12 alkyl or alkoxy.
• R t and R 2 are independently C 3 -C ⁇ , 2 alkyl or alkoxy, x is 1 and F may be on any ofthe available substitution positions on the phenyl ring specified.
• R and R 2 are independently C 3 -C 12 alkyl or alkoxy.
• R is C 3 -C 12 alkyl and R 2 is given by the general formula (CH 2 ) n -CHXCH 2 CH 3 , where n is 1 to 5 and X is CN or Cl .
• R, and R 2 are independently C,-C 15 alkyl.
• R ⁇ and R 2 are independently C 3 -C 9 alkyl.
• thermochromic devices for example those devices described by D. G, McDonnell in Thermochromic Liquid Crystals, Critical Reports on Applied Chemistry, vol. 22, edited by G.W. Gray, 1987 pp 120-44 and references therein.
• the materials described by the current invention may be inco ⁇ orated into electrochemical devices. Further, the materials may be processed as thin and flexible films for use in various applications such as thin-film batteries and afford high anisotropic conductivity.
• An electrochemical device inco ⁇ orating materials ofthe present invention is described in Figure 6.
• An electrochemical device consists of an anode 20, typically made from metal and a cathode 21 preferably a composite cathode (see Scrosati et al in Applications of Electroactive Polymers, Ed. B. Scrosati, Chapman & Hill, London 1993. Between the anode 20 and cathode 21 is sandwiched an electrolyte 22 which is typically made from a polymer matrix that is doped with one or more ionic compounds (i.e. salts) containing cations which are mobile in an applied electric field.
• ionic compounds i.e. salts
• High conductivity may be obtained by using an appropriately selected concentration of charge carriers achieving a high ionic conductivity - see Bruce et al in J. Chem.
• Conductivity may be promoted by using polar polymers which show high dielectric constants.
• the salts which may be used may be chosen from any ofthe known types including those that possess silver or lithium ions, e.g. LiBF 4 , LiClO 4 , LiSO 3 CF 3 , Li(NSO 2 CF 3 ) 2 .
• Thin films of electrolytes may be prepared by pouring a solution of polymer and salt into a mould and controlling the rate of evaporation of the solvent - see Scrosati et al in Applications of Electroactive Polymers, Ed. B. Scrosati, Chapman & Hill, London 1993.
• This technique may be varied by spin coating ofthe polymer/salt solution under a constant nitrogen stream in a centrifuge on a flat non-tacky substrate. This technique may be used to produce free- standing, macroscopically ordered liquid-crystalline polymeric films.

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